1. Field of the Invention
The present invention relates to a magnetic tape drive device, and more particularly to a magnetic tape drive device for driving a magnetic tape of the cartridge type with a capstan to run.
2. Related art
A conventional magnetic tape drive device M, as shown in FIGS. 9A and 9B, includes a rotor case 3, shaped like a tube with the bottom, and a stator core 5. The rotor case 3 is coupled with one end portion of a rotary shaft 1 by means of a bracket 2. A drive magnet 3a is secured to the inner surface of the rotor case 3. The stator core 5, secured to a base board 4, is wound by coils 5a, which is disposed facing the drive magnet 3a. Current flowing through the coil 5a and a magnetic field developed by the drive magnet 3a cooperate to turn the rotary shaft 1 together with the rotor case 3. A rubber roller 7 is fastened to the other end of the rotary shaft 1 protruded from the base board 4, with a spacer 6 intervening therebetween. The rubber roller 7 is brought into contact with a capstan roller 9 of a tape cartridge 8. With this structure, when the rotary shaft 1 is turned, the capstan roller 9 is turned.
In the magnetic tape drive device M thus constructed, many parts are required for constructing a mechanism for transmitting a turning effect of the rotary shaft to the capstan roller 9. This increases the cost to manufacture. Further, the required height h of the magnetic tape drive device hinders the thinning of the whole device.
With the structure of fastening the rubber roller 7 to the rotary shaft 1 of a small diameter, an efficient transmission of the torque of the rotary shaft 1 to the capstan roller 9 in a state that a load to the rotary shaft 1 is minimized, inevitably requires reduction of the diameter of the rubber roller 7.
As the result of the diameter reduction of the rubber roller, a contact area of the rubber roller 7 with the capstan roller 9 is reduced. A slip tends to occur in the relative motion of the rubber roller to the capstan roller. To cope with this, approach to increase a contact force is allowed. In the approach, a side pressure to the rotary shaft 1 (pressure acting in the direction orthogonal to the axial line) increases, so that the torque transmission is inefficient. Thus, a proper setting of the contact pressure is difficult, making the assembling work difficult and inefficient.